Technical Piston damage

I know there are some engine wizards here on the HAMB and I am having a discussion about these marks on pistons. Over the years I have seen this damage to pistons many , many times, but never figured out exactly what caused it. It’s those “ marks, scratches, scoring” or what ever you want to call it above the top ring!
Here is a picture of a piston with this damage, any thoughts on this? Thanks in advance,




Bones

 

I've seen that on a lot of engines, and maybe more often on small air cooled stuff like single cylinder Kohlers and such. I figured it was from hard carbon buildup in the ring ridge area, and bore/skirt wear allowing the piston to rock a bit. Maybe I'm wrong...just my thoughts.

 

either dirt or carbon particles getting caught in there and scoring it?

I don't know...

 

Thrust side only? Foreign Object Damage perhaps. Could definitely be carbon build up breaking free.

 

Based on the skirt of this piston, I believe it saw a pretty good overheat. When an engine overheats, the pistons swell and begin to rub the cylinder wells hard enough to break down the lube layer. I would expect to see cylinder wall scoring also. The upper scoring is from hard carbon particles and again an overheat.

 

I'm with @jaracer on the heat thing. It'll either be that or a piston that wasn't properly fitted to a cylinder with finish honing. Seen plenty of guys have a block bored to say 30 over without providing pistons and then take it home and slap out of box pistons in no hone. Buddy did that on a 283 and had a persistent issue where it'd run fantastic till it got close to temp. Then the engine would just slow down and stop

 

What does the top of the piston look like?

 

Thanks guys, I also think it is carbon coming loose and “ wedging “ itself in between the top of the piston and the cylinder . That is why you only see it above the top ring, the ring will not let the carbon particles get past it. Also the damage is concentrated in that small area on the piston, so you get obvious damage, but the scratches are spread out over 3to 4 inch on the cylinder, so they appear less.
This was my opinion, just though I would see what others thought.
James, that is only a picture of some one else’s piston that I used, I don’t have a picture of the top of it.





Bones